1. Field of the Invention
The present invention relates to a multi-optical-path photoelectric safety apparatus having a light emitting unit and a light receiving unit. More particularly, the present invention relates to a multi-optical-path photoelectric safety apparatus comprising a muting function.
2. Discussion of the Related Art
A multi-optical-path photoelectric safety apparatus is provided to ensure worker safety when using an apparatus involving a source of danger, such as a pressing machine. The multi-optical-path photoelectric safety apparatus comprises a light emitting unit and a light receiving unit. The light emitting unit comprises a large number of light emitting elements arranged in a row. The light receiving unit comprises a corresponding number of light receiving elements as the number of the light emitting elements, and they are also arranged in a row. The light emitting and receiving units form a protective barrier by making a light curtain. When a light blocking substance through which light cannot transmit enters a detection area of the protective barrier, the operation of the machine is forcibly stopped.
In a pressing or other machine it is necessary to carry a workpiece in and carry the post-worked workpiece out. Thus, the workpiece needs to be passed through the light curtain. The multi-optical-path photoelectric safety apparatus comprises a muting function to allow the workpiece to pass through the light curtain. That is, the muting function temporarily makes the protection function of the multi-optical-path photoelectric safety apparatus ineffective when the workpiece passes through the light curtain.
FIG. 15 shows an outline of a multi-optical-path photoelectric safety apparatus comprising a muting function in a related art device. In the related art example, a light emitting unit 2 and a light receiving unit 3 are installed on either side of a conveyor line 1 carrying a workpiece into a pressing machine.
The conveyor line 1 is provided with workpiece detection sensors 4 for detecting a workpiece W passing through a light curtain. When the workpiece W is detected, the muting function is started. During the muting function in the related art device, all of the detection areas of the light curtain formed between the light emitting unit 2 and the light receiving unit 3 become ineffective.
The muting function removes the essential protection function from the multi-optical-path photoelectric safety apparatus although this protection function is only removed temporarily. However, removing the protection function of all of the detection areas of the light curtain when the muting function is operated is not preferred.